1. Field of the Invention
The present invention relates to a power window apparatus with a function to detect a foreign object caught in the window, and particularly to a power window apparatus which shortens the non-detection time in the motor startup period and can detect an object caught in the window even during the motor startup period.
2. Description of Related Art
A conventional car power window apparatus with a function to detect a foreign object is known where, if it detects a foreign object caught in a window during a manual or automatic closing operation of the window, it stops the movement of the window immediately or moves the window in the window opening direction.
The conventional power window apparatus uses motor load current values as parameters for detection of a foreign object caught in the window (this type of apparatus is hereinafter called a xe2x80x9cload current based typexe2x80x9d). In this apparatus, the whole window moving range is divided into multiple moving subdivisions and a reference current value indicating whether a foreign subject is caught in the window or not is preset for each moving subdivision; as the window moves through each of these subdivisions, the motor load current value detected in the subdivision is compared with the reference current value preset for that subdivision and if, as a result of comparison, the motor load current value is found to considerably exceed the reference current value, the apparatus concludes that a foreign object has been caught in the window and immediately stops the movement of the window or moves the window in the window opening direction.
In this power window apparatus, reference current values to be preset for the multiple moving subdivisions are determined as follows: as the window moves through the subdivisions, the peak motor load current for each of such subdivisions is measured in the condition that nothing is caught in the window. The reference current value for a subdivision is thus determined according to the measured peak current value for that subdivision.
Among known power window apparatuses capable of detecting a foreign object, there is a type which uses motor load torques as parameters for foreign object detection instead of motor load current values (this is hereinafter called a load torque based type.).
In the load current based type of power window apparatus or the load torque based type of power window apparatus, when the motor for opening/closing the window is started, initially the load current which flows through the motor transitionally fluctuates or the load torque which is generated from the motor transitionally fluctuates and therefore the load current value or load torque value measured during the period of transitional fluctuation is not a stable, correct value and cannot be used to detect a foreign object caught in the window correctly. Therefore, in the load current based type of power window apparatus or the load torque based type of power window apparatus, an operation to detect a foreign object caught in the window is not performed during the period of instability (motor startup period) from the start of the motor until the motor load current value or motor load torque value is stabilized or becomes almost constant, but such an operation is performed just after completion of this period of instability.
In the load torque based type power window apparatus in particular, the motor load torque may fluctuate to a relatively large degree during the period of instability, or this period of instability, which lasts until the motor load torque becomes almost constant, may be prolonged.
In other words, for the load torque based type of power window apparatus, the amount of motor load torque variation in the motor startup period varies depending on the following factors: the starting torque characteristic of the motor in use; the structure of the window moving mechanism including the window to be driven by the motor; the type of car; the number of years when the car has been used; the external conditions or environment in which the car is used, and other factors. In addition, the length of the period of instability until the motor load torque becomes almost constant varies as well.
FIG. 4 is a characteristic graph showing an example of the relation between the number of pulses and the motor load torque in the motor startup period in three motors and window moving mechanisms which are arbitrarily chosen; and FIG. 5 is a characteristic graph showing an example of the relation between the number of pulses and the motor load torque in the motor startup period at different ambient temperatures for a motor and its window moving mechanism.
For three arbitrarily chosen motors A, B and C, the characteristic curves of motors A, B and C are represented by a, b and c, respectively, as shown in FIG. 4. From this figure, the characteristics of motors A, B and C in the startup period may be compared and described as follows. The characteristic curve a for the motor A shows that the variation in motor load torque is the largest and the period of instability (a period required until the motor load torque becomes almost constant) is the longest, and the end of the period of instability is just before pulse number 200; the characteristic curve b for the motor B shows that the variation in motor load torque is smaller than in the characteristic curve a and the period of instability is shorter than in the characteristic curve a, and the end of the period of instability is slightly beyond pulse number 150; and the characteristic curve c for the motor C shows that the variation in motor load torque is the smallest and the period of instability is the shortest, and the end of the period of instability is before pulse number 150.
Namely, the motor load torque variation in the motor startup period and the length of the period of instability (a period which lasts until the motor load torque becomes almost constant) differ among these motors and window moving mechanisms for opening/closing the windows. It may also be said that the motor load torque variation and the period of instability differ among any other chosen motors and window moving mechanisms.
The characteristic curve of a chosen motor D at an ambient temperature of 100xc2x0 C. and that at an ambient temperature of xe2x88x9240xc2x0 C. are represented by d1 and d2, respectively, as shown in FIG. 5. The characteristic curve d1 concerning the startup period for motor D shows that the variation in motor load torque is larger and the period of instability (a period required until the motor load torque becomes almost constant) is longer, and the end of the period of instability is slightly beyond pulse number 150; on the other hand, the characteristic curve d2 shows that the variation in motor load torque is smaller than in the characteristic curve d1 and the period of instability is slightly shorter than in the characteristic curve d1, and the end of the period of instability is before pulse number 150.
This means that even in the same motor and window moving mechanism used for opening/closing the window, the motor load torque variation in the motor startup period and the length of the period of instability (a period which lasts until the motor load torque becomes almost constant) differ depending on the external conditions or environment in which they are used.
For the above reason, in the load torque based type of power window apparatus, the time to start detection for a foreign object caught in the window is preset to a time when most motors have ended their period of instability and have entered the period of stability (for example, a time when pulse number 200 is reached as shown in FIG. 4), because the load torque characteristic in the motor startup period differs among motors and window moving mechanisms for opening/closing the window, as discussed above.
For the abovementioned load torque based type of power window apparatus, in which the time to start detection for a foreign object in the window is preset to a time when most motors have ended their period of instability and entered the period of stability, the non-detection period, or a period from the start of the motor to the start of detection for a foreign object is relatively long; if a foreign object is caught in the window during this non-detection period, it cannot be detected and thus no countermeasure cannot be taken.
In view of the abovementioned technical background, it is an object of the present invention to provide a power window apparatus which shortens the non-detection period from the start of the motor to the start of detection for a foreign object as much as possible and thus decreases the probability of a foreign object being caught in the non-detection period.
In order to achieve the abovementioned object, according to one aspect of the present invention, the power window apparatus with a function of foreign object detection comprises: a motor for opening or closing the window; a motor driver for driving the motor; a pulse generator for generating pulses corresponding to a run of the motor; a memory for storing various values to be preset; a micro control unit for overall drive control; and a window operation switch for opening and closing the window. Here, the micro control unit detects a value of motor load torque applied to the window at the time of opening or closing it and compares the value of motor load torque with a reference value stored in the memory. If the value of motor load torque is larger than the reference value by a prescribed amount, the micro control unit concludes that there is a foreign object caught in the window and stops or reverses the motor through the motor driver and inactivates the function of foreign object detection until a transitional period of motor load torque fluctuation from the start of the motor is over. The power window apparatus further comprises a timer. Here, a permissible variation range in the value of motor load torque and a maximum successive number, which are used to determine the end of the transitional period of motor load torque fluctuation, are stored in the memory.
The micro control unit comprises a control processor by which a variation in the value of motor load torque per unit time is monitored from the start of the motor using the timer, and by which, when it is found that a number of successive torques which the variation in the value of motor load torque fall within the permissible variation range has reached the preset maximum successive number, it is concluded that the time to end the transitional period of motor load torque fluctuation has been reached and the function of a foreign object detection is activated.
It is desirable that the permissible variation range and maximum successive number which are stored in the memory of the above apparatus are determined for each motor in use according to an actually measured starting characteristic of the motor.
According to another aspect of the present invention, for each motor in use, the permissible range of motor torque variation per unit time and the maximum number of successive torques which fall within the permissible variation range are previously stored in the memory; when the motor is started, the motor torque variation per unit time is compared with the permissible range of motor torque variation per unit time stored in the memory; when the variation comes to fall within the permissible range, how many times a torque within the permissible variation range is produced successively is detected, and when the number of such detected torque values exceeds the maximum successive number stored in the memory, it is concluded that the transitional period of motor load torque fluctuation has ended, and the function to detect a foreign object caught in the window is immediately activated. Therefore, the non-detection period (namely, a period from the start of the motor until the start of foreign object detection) is shorter than in the conventional apparatus, thereby reducing the probability of a foreign object being caught in the window during the non-detection period.